Vattenfall runs tests at Kruemmel, seeks outage cause

* Vattenfall has to replace two transformers

* Kruemmel case unleashes debate about nuclear energy

BERLIN, July 9 (Reuters) - Swedish-German utility Vattenfall AB [VATN.UL] said on Tuesday the reason for a failed restart at its Kruemmel nuclear plant on Saturday was unclear but it was making thorough checks of all its processes.

The plant has to replace two transformers after the incident, which caused power outages in northern Germany, and the firm says it will stay offline for at least several months.

Under normal circumstances, Vattenfall would not expect the new transformers to arrive before next April after which time it would have to be allowed to install them, its officials said.

"Now all processes -- technical and organisational -- are being tested," said Vattenfall-Europe chief Tuomo Hatakka at a news conference in Berlin.

"This incident has deeply shocked me but it has not paralysed me," he said. "We are aware that we have lost trust over this. We have to earn it back again," he said.

The standstill is costing the company several hundreds of thousands of euros a day in lost revenue.

The incident at Kruemmel, which had been down for two years due to safety issues, has fed into a heated political debate about nuclear energy before September's federal election.

The anti-nuclear Social Democrats (SPD), who share power with Chancellor Angela Merkel's conservatives in a loveless coalition, have jumped on the failed restart to increase calls for an accelerated phase out of Germany's nuclear plants.

Merkel's conservatives, forced to go along with the phase out in the 2005 coalition deal with the SPD, want to prolong the running times of those plants judged safe.

However, analysts say the Social Democrats are unlikely to gain from the issue, not least as Germans' aversion to atomic energy is waning due to higher prices and energy supply fears.

Vattenfall has been criticised for its handling of the incident and Sweden on Wednesday demanded the firm provide an account of its work on nuclear safety after the Kruemmel incident and security concerns in Sweden.

Vattenfall peer E.ON (EONGn.DE) owns a 50 percent stake in Kruemmel but has said it has no reason to pull out of the troubled station. (Reporting by Markus Wacket and Vera Eckert; writing by Madeline Chambers; editing by James Jukwey)